﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!!");
            Console.WriteLine("请输入圆的半径：");
            double r = double.Parse(Console.ReadLine());
            double circle = R * R * 3.14;
            Console.WriteLine("圆的面积是：" + circle);
            Console.ReadLine();
        }
    }
}
